Mutation of a conserved proline disrupts the retinal-binding pocket of the X-linked cone opsins.
OBJECTIVE
To test the effects of disruption of a conserved proline in the green cone opsin molecule on light-activated isomerization, transducin activation, protein accumulation, glycosylation, and transport.


METHODS
Stable cell lines were established by transfecting EBNA-293 cells with a plasmid containing wild-type or mutant (P307L) green opsin cDNA molecules. The proteins were induced by culturing the cells in the presence of CdCl2 and analyzed by spectra, transducin activation, Western blotting, and immunocytochemistry.


RESULTS
The P307L mutation diminished ability of the visual pigment to absorb light at the appropriate wavelength and to activate transducin. Protein glycosylation and transport to the cell membrane were unaffected. Although there was some diminution in the accumulation of the opsin, this was insufficient to account for the observed effect.


CONCLUSIONS
Like rhodopsin, the formation of the cone opsins visual pigments is dependent on the binding of retinal into a hydrophobic pocket that is formed by the second and fourth transmembranous loops. Disruption of a conserved proline near the retinal binding site represents a cause of color vision deficiency that is unrelated to spectral shifts of the photopigment.
Ostrer
H
H
Human Genetics Program, Department of Pediatrics, New York University Medical Center, New York, NY 10016, USA. ostreh01@mcrcr6.med.nyu.edu
Kazmi
M A
MA
D001692:Biological Transport; D015153:Blotting, Western; D002478:Cells, Cultured; D008040:Genetic Linkage; D006031:Glycosylation; D006801:Humans; D007150:Immunohistochemistry; D016296:Mutagenesis; D011392:Proline / Q000235:genetics*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism / Q000502:physiology*; D017299:Rod Opsins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013057:Spectrum Analysis; D015293:Transducin / Q000378:metabolism; D014162:Transfection; D014960:X Chromosome
D017299:Rod Opsins; D011392:Proline; D015293:Transducin